APK Studio

Open-source, cross platform Qt based IDE for reverse-engineering Android application packages. It features a friendly IDE-like layout including code editor with syntax highlighting support for *.smali code files.

Downloads / Source

If you are just willing to quickly decompile an Android app, you can make use of DeAPK - Online APK Decompiler which lets you decompile an Android app using apktool and jadx.

Developed & maintained by Vaibhav Pandey -aka- VPZ along with contributor(s).